Chapter 11 - Principles of Disease and Epidemiology

1. Chapter 11 - Principles of Disease and Epidemiology • Pathology Study of disease • Etiology Study of the cause of a disease • Pathogenesis Development of disease • Infection Colonization of the body by pathogens • Disease An abnormal state in which the body is not functioning normally

2. Normal Microbiota and the Host • Transient microbiota may be present for days, weeks, or months • Normal microbiota permanently colonize the host • Symbiosis is the relationship between normal microbiota and the host

3. Normal Microbiota and the Host: • In one organism is benefited and the other is unaffected. • In both organisms benefit. • i.e. E. coli produces vitamin K (and some B) • In parasitism, one organism is benefited at the expense of the other.

4. Normal Microbiota and the Host: • Locations of normal microbiota on and in the human body Figure 14.2

5. Normal Microbiota and the Host: • Microbial antagonism is competition between microbes. • Normal microbiota protect the host by: • occupying niches that pathogens might occupy • producing acids • producing bacteriocins

6. Normal Microbiota and the Host: • Some normal microbiota are opportunistic pathogens. • (vaginal yeast infection) • Normal location: vagina, mouth • (urinary tract infections) • Normal location: large intestine

7. Normal Microbiota and the Host: • (hospital acquired diarrhea; may cause pseudomembranous colitis) • Normal location: large intestine • (a major cause of meningitis) • Normal location: nasopharynx

8. are live microbes applied to or ingested into the body, intended to exert a beneficial effect. • are chemicals used to promote growth of beneficial microbiota

9. Classifying Infectious Diseases • Symptom A change in body function that is felt by a patient as a result of disease • Sign A change in body function that can be measured or observed as a result of disease. • Syndrome A specific group of signs and symptoms that accompany a disease.

10. Classifying Infectious Diseases • Communicable disease A disease that can be spread from one host to another. • Contagious disease A disease that is easily spread from one host to another. • Noncommunicable disease A disease that is not transmitted from one host to another. • i.e. Chicken pox, measles, common cold are contagious • i.e. Tetanus, Anthrax are noncommunicable

11. Occurrence of Disease • Incidence Number of new cases of a disease during a specific time period. • Prevalence Total number of old and new cases of a disease during a specific time period. • Sporadic disease Disease that occurs occasionally in a population. • i.e. Eastern Equine Encephalitis

12. Occurrence of Disease • Disease constantly present in a population. i.e. common cold • Epidemic disease Disease acquired by many hosts in a given area in a short time. i.e. influenza, • Pandemic disease Worldwide epidemic. i.e. influenza; AIDS • Immunity in most of a population.

13. Severity or Duration of a Disease • Acute disease Symptoms develop rapidly, but last a short time. i.e. influenza, cold • Chronic disease Disease develops slowly, lasts a long time. i.e. Hepatitis B • Subacute disease Symptoms between acute and chronic. i.e. gingivitis • Latent disease Disease with a period of no symptoms when the “microbe” is inactive. i.e. genital herpes,

14. Extent of Host Involvement • Local infection Pathogens limited to a specific area of the body. i.e. pulmonary Tuberculosis; Strep throat • Systemic infection An infection throughout the body. • Focal infection Systemic infection that began as a local infection. i.e. Tuberculosis; Tetanus • Bacteremia Bacteria in the blood • Septicemia Growth of bacteria in the blood

15. Extent of Host Involvement • Toxemia Toxins in the blood • Viremia Viruses in the blood • Primary infection Infection that causes the initial illness; often acute • Secondary infection Opportunistic infection after a primary (predisposing) infection

16. The Stages of a Disease Figure 14.5

17. Reservoirs of Infection • Reservoirs of infection are the primary receptacles of the infectious agent. They may or may not be the direct source of the infection. • Animal • dogs, bats, racoons, foxes, other mammals • Rocky Mountain Spotted Fever: ticks • soil, infected cows, sheep, other animals • may be transmitted to humans

18. Reservoirs of Infection • Human — HIV, gonorrhea • Carriers may have inapparent infections or latent diseases • Nonliving — • Soil: Botulism (Clostridium botulinum), Tetanus (Clostridium tetani) • Water: Cholera (Vibrio cholerae) • Food: Tapeworm

19. Transmission of Disease • Contact • Direct Requires physical contact between infected and susceptible host • Indirect Spread by • Droplet Transmission via airborne droplets; usually travel less than one meter

21. Transmission of Disease • Vehicle Transmission by an inanimate reservoir (food, water, air) • Vectors Insects, especially fleas, ticks, and mosquitoes • Insect carries pathogen on feet. • Pathogen reproduces in vector. i.e. Malaria, Rocky Mountain Spotted Fever disease

23. Nosocomial (Hospital-Acquired) Infections • Are acquired as a result of a hospital stay • 5-15% of all hospital patients acquire nosocomial infections • A leading cause of death in U.S. Figure 14.7, 9

24. Relative frequency of nosocomial infections

25. Common Causes of Nosocomial Infections

26. Emerging Infectious Diseases • Diseases that are new, increasing in incidence, or showing a potential to increase in the near future. • Contributing factors: • Evolution of new strains • Inappropriate use of antibiotics and pesticides • Antibiotic/pesticide resistant strains • Changes in weather patterns (and global warming?) • (and malaria)

27. Emerging Infectious Diseases • Contributing factors: • Modern transportation • Ecological disaster, war, expanding human settlement • Ebola • Animal control measures • Public Health failure • Diphtheria

28. Epidemiology • The study of where and when diseases occur • How they’re transmitted • How many infected Figure 14.11

29. Epidemiology

32. Table 14.7

33. Centers for Disease Control and Prevention (CDC) • Collects and analyzes epidemiological information in the U.S. • Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov • Morbidity: incidence of a disease • Mortality: death from disease